Field of the Invention
This invention relates to a power transmission belt using twisted cords of synthetic fiber or inorganic fiber as load-carriers.
Description of the Prior Art
With the recent trend to fuel expenses saving and higher efficiency in the automobile field, it has been required that the power transmission belt to be used for automobiles stands the use under severe conditions, for example, the V-ribbed belt to be used as a fan belt of motor car must be usable under the high speed condition (for example, at around 60 m/second).
Under such high speed condition, however, the belt oscillates in width direction about 30-60 mm and if such oscillation continues for many hours, the following troubles are liable to occur.
(i) Generation of abnormal sound due to oscillation. PA0 (ii) Extraordinary wear of belt due to pulley. PA0 (iii) Belt slip attributable to the decrease in tension originating from the wear of belt. PA0 (iv) Degradation of rubber caused by abnormally high temperature due to slip. PA0 (v) Coming off of projecting parts of belt. PA0 (i) To change the direction of warp of upper canvas. PA0 (ii) To embed load-carrying cords of S-twist and those of Z-twist alternately. PA0 (iii) To lessen winding pitch and winding angle of load carrier.
As measures to cope with such oscillation of belt, various methods have been known, for example,
However, from the method (i) fully satisfactory result cannot be obtained. In the method (ii) load-carrying cords of different twisting direction must be manufactured. In this case, since load-carrying cords of S-twist and those of Z-twist turn in reverse direction with each other at molding of a belt, a belt of disordered cord winding pitch is produced and such belt is short in service life. In the method (iii) load-carrying cords are closer to each other and consequently adhesiveness of them is reduced considerably. Although such trouble can be eliminated by reducing the diameter of each load-carrier, the desired tensile strength of a belt as a whole cannot be obtained from load carriers of smaller diameter.
After ardent studies, the inventors have found that the first twist multiplier and especially the angle of final twist affect the oscillation of a running belt to a large extent and such findings have led them to develop the present invention.
U.S. Pat. No. 4,083,260 discloses an endless power transmission belt comprising a tension section, a compression section and a load-carrying section between the foregoing two sections, wherein such load-carrying section has a twisted, helically wound load-carrying cord disposed therein which is defined in terms of twist multiplier having a numerical value in the range of between 4-8 in the equation TM=td1/2/K (where TM is the twist multiplier, t is the number of twists of the cord expressed in terms of the number of twists per inch, d is denier of the cord, and K is constant for the particular material used to define the cord). Japanese Patent Application Publication No. 56-105135 discloses a power transmission belt having load carriers which are fraying-free twisted cords of aramid fiber having the twist multiplier of 3-9, Japanese Patent Application Publication No. 59-19744 teaches a power transmission belt having load carriers of improved fatigue resistance which are twisted cords of glass fiber made by final twisting a plurality of glass fiber strand which were first twisted in the same direction as final twisting, with the final twist multiplier of 0.60-1.50 and the first twist multiplier which is 1/4-1/2 of the final twist multiplier. None of these belts, however, is sufficient in preventing oscillation of a belt in its width direction.